Inorganic materials such as quartz glass, multi-component glass or the like, which are characterized by a low optical transmission loss and a wide transmission band, have been widely used as a base material for optical components or optical fibers. Recently, polymer materials have also been developed and are made attractive as materials for optical waveguides because they are superior in workability and cost as compared to the inorganic materials. For example, proposed is a flat plate type optical waveguide having a core-clad structure where a core is formed of a polymer with an excellent transparency, such as polymethyl methacrylate (PMMA) or polystyrene, and a cladding material is formed of a polymer having a refractive index lower than that of the core material (Patent Document 1). On the other hand, a flat plate type optical waveguide with lower loss has been realized by using a polyimide which is a transparent polymer of high thermal resistance (Patent Document 2).
As one of applications of a polymer optical waveguide, an optical and electric combined board is considered. It is a substrate in which an optical waveguide layer is formed in an upper layer, a lower layer or an inner layer of a printed wiring board. At this time, it is important to develop a method for optical coupling between a surface type optical element and an optical waveguide layer to be mounted on the optical and electric combined board. Since the optical axis of the surface type optical element and that of the optical waveguide layer are different by 90 degrees, there is a need to perform a 90 degree optical path conversion. As the method for optical path conversion, there has been proposed a short optical fiber or a short optical waveguide (each generally called an optical pin) for linking between the surface type optical element and the optical waveguide layer (Non-patent Document 1). When an optical pin is used, accuracy in the position alignment between the optical pin and the optical waveguide layer becomes important. So, in order to align the position, a position alignment guide is prepared with high accuracy at a position different from that of the core of the optical pin such as a connector, and a method for aligning the position with the help of the guide is considered. However, since length accuracy of the optical pin, respective dimensional accuracy of the guide and the guide hole, position accuracy of the guide and the core, and the like are required to be high, the cost involved in forming the guide might possibly be increased. Furthermore, when the optical pin is formed in a shape of a connector, it becomes difficult to mount the surface type optical element or other elements thereon.
Patent Document 1: Japanese Patent Laid-open No. 1991-188402
Patent Document 2: Japanese Patent Laid-open No. 1992-98072
Non-patent Document 1: The Institute of Electronics, Information and Communication Engineers Transactions 2001/9, Vol. J84-C No. 9, pages 724-725